The invention relates to a parking lock for automatic transmissions of motor vehicles where the output of the transmission is blocked by a locking pawl engaging in a parking interlock gear, the latter thus being protected against torsion.
DE 43 17 257 describes a parking lock for automatic transmissions of motor vehicles where a locking pawl is drawn out from the parking interlock gear by a cylinder being filled with pressurized oil and the piston thereof moving a connecting rod against spring tension via a gate member. By manually moving a hand lever via an operative connection, the connecting rod with the locking pawl can be moved in the gate member and the parking lock is thus unlocked. By the piston rod having a direct connection with the connecting rod of the locking pawl and thus a linear movement being directly transmitted to the connecting rod, via a linearly moved gate member, the operative connection, which also carries out a linear movement since it ends in the passenger space of the vehicle, has to be expensively sealed in the automatic transmission. Should the parking lock be hydraulically unlocked, the locking pawl is drawn out from the parking interlock gear by the connecting rod carrying out a linear motion which is drawn back by a pin passed in a diagonally extending groove of the gate member. Thereby considerable frictional forces appear between the pin and the diagonally extending groove. If the parking lock is manually unlocked in an emergency and the pin engages in the gate member, this position can again be disengaged by the piston of the hydraulic unit being loaded with pressure and the pin being enabled to leave the engagement. In this state, the possibility exists that the pin impinges upon the forking of the grooves in the gate member and being sheared off at the same time. By using a gate member, there is, likewise, the possibility that jerks during driving produce an undesired operation of the parking lock device, since a linearly supported gate member constitutes a spring-mass system which reacts to linear forces.
The invention is based on the problem of providing a parking lock for an automatic transmission of a motor vehicle which stands out by great operational security, simple construction, reliable sealing and low friction.
The parking lock comprises a fixture which is connected with a connecting rod having a locking pawl and is moved by a hydraulic actuating device comprised of one piston, one cylinder and one recoil spring. The fixture consists of two discs which are disposed on a common shaft and by rotation of the discs operation of the parking lock can be actuated. The first disc, here called the detent disc, has a first, eccentrically mounted connection to a connecting rod having a locking pawl, and, opposite to the first connection and eccentrically disposed, a second connection to a hydraulic actuating device. If the hydraulic actuating device is actuated, the parking lock is locked and unlocked exclusively by the rotary motion of the fixture. A second disc, here called the emergency release disc, has, via a pivot which can move in a groove in the detent disc, a connection to the detent disc, and a connection via a central shaft, with which the emergency release disc is non-rotatably connected, and upon which the detent disc is rotatably supported, which shaft is connected outside the transmission via a seal in the housing of the transmission with an operative connection for the emergency release. The emergency release disc rotates within to stop and automatically come to a position in which the parking lock is unlocked, via the emergency release, and thus the rotation of the emergency release disc and, via the pivot, the rotation of the detent disc, and by a detent unit, preferably a spring, is kept in this position until this position is again turned back to the initial state by rotation of the first disc by automatic unlocking of the detent. By the fact that the discs carry out a clear rotary motion, it is possible to easily support the central shaft of the discs in the housing of the automatic transmission and because the shaft is passed outwardly through the housing of the automatic transmission, an operative connection can be easily attached and the shaft sealed in the housing for reliable operation. By not using any masses which have to be linearly moved, the invention operates reliably even under great shock loads.